This invention relates generally to x-ray scattering detectors wherein incident x-rays are scattered by the electrons of a sample specimen under investigation and is particularly directed to apparatus for time-resolved measurement of small-angle scattered x-ray intensity by complex molecules such as proteins.
Small-angle X-ray scattering (SAXS) detectors are increasingly being used for the analysis of the composition and characteristics of materials in solid, liquid or vapor form. For example, SAXS is used in protein science for characterizing the conformational states of proteins and the kinetics of protein refolding by using an intense x-ray beam focused on a protein sample in solution. The electrons of the sample under investigation scatter a portion of the flux of the incident x-ray beam and the scattered x-ray beam intensity is measured as a function of the scattering angle. From the x-ray scattering data, the protein""s overall size (radius of gyration), overall shape (pair distribution function) and association state may be determined. This type of SAXS analysis is currently the only known time-resolved approach capable of determining these values.
In the field of SAXS material analysis, however, there is a problem with optimization of the time/rate of data acquisition. More specifically, current SAXS detectors are typically modified x-ray crystallography detectors which are not optimized for SAXS data acquisition. There is thus a need to improve the performance and capabilities of SAXS material analysis by providing a fast detector capable of accurate time resolution specifically designed for use in SAXS applications.
The present invention addresses the aforementioned limitations of the prior art by providing apparatus for directing an x-ray beam onto a specimen under investigation and then detecting the x-rays scattered by the specimen after transiting an evacuated tube. A flat, disc-shaped detector provided with a fluorescent screen and concentric rings of first fiber optic bundles is disposed on the distal end of the tube for detecting x-rays scattered over small angles, and an annular detector also incorporating a fluorescent screen and second fiber optic bundles is concentrically disposed about an intermediate portion of the tube for detecting x-rays scattered over larger angles.
Accordingly, it is an object of the present invention to provide an arrangement for detecting x-rays scattered at small angles from a material being analyzed having high resolution and a wide dynamic range of measurement of momentum transfer of the incident x-rays.
It is another object of the present invention to provide for the more efficient detection of x-rays scattered over small angles by a material being analyzed such as a large, complex protein molecule on a time-resolved basis.
A further object of the present invention is to provide a fast detector for the time resolution measurement of the intensity of x-rays scattered over small angles by a complex molecule such as naphthalene in a gas phase sample.
This invention contemplates apparatus for detecting small-angle scattering of x-rays by a specimen being analyzed, the apparatus comprising an evacuated, cylindrical tube having a longitudinal axis and first and second opposed ends disposed on the axis, wherein x-rays are directed along the axis and onto the specimen disposed adjacent the tube""s first end; a first detector disposed on the second end of the tube for detecting x-rays scattered by the specimen over a first angular range relative to the longitudinal axis of the tube; and a second detector disposed concentrically about and intermediate the first and second ends of the tube for detecting x-rays scattered by the specimen over a second angular range, wherein the second angular range is greater than the first angular range.